simplify HHWheelTimerBase catch
simplify HHWheelTimerBase catch

Summary: Just need a catch-all `catch` clause. And use `exceptionStr` to include the type of the thrown object.

Reviewed By: luciang

Differential Revision: D40659816

fbshipit-source-id: 73eb47d93eafdb48c932bec7575b88def990202b

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly